It is well known to use a solid catalyst component comprising a magnesium halide, and supported thereon, a titanium compound containing at least one Ti-halogen bond and an electron-donating compound for producing olefin polymers.
Particularly, European patent application No. 361,494 reported that the use of certain diether compounds as an electron-donating compound (an internal donor) provides a highly active catalyst even without using another electron-donating compound (an external donor). Furthermore, the addition of an external donor, such as an organic silicon compound, a diether compound, a nitrogen compound or a carboxylate compound, to the above catalyst, allows one to obtain a polymer with very high level of stereo-regularity while maintaining high catalytic activity (EP 728769).
It is also recognized that an alikoxyester compound is effective as the internal donor of olefin polymerization catalysts (EP 383346). Furthermore, it is reported that when the alkoxyester is employed as an external donor for a catalyst using a phthalate or ketoester compound as an internal donor, the catalyst provides a polymer having excellent polymer properties (EP704424). It is however always felt the need of improved catalysts systems with high activity and good hydrogen response during polymerization, and capable to produce an olefin polymer having a very high stereo-regularity.